Protective immunity of sevenband grouper, Epinephelus septemfasciatus Thunberg, against experimental viral nervous necrosis

This paper describes the protective immune responses of sevenband grouper, Epinephelus septemfasciatus Thunberg, immunized with live piscine nodavirus , the causative agent of viral nervous necrosis (VNN), or the Escherichia c oli - expressed recombinant coat protein. Nodavirus-neutralizing antibodies were detected at titres ranging from 1:158 to 1:1257 in serum of sevenband grouper which survived intramuscular injection with the virus, by a cell c ulture assay system. The virus-neutralizing ability of immune serum was als o confirmed by injecting virus previously treated with serum into fish. Thi s indicates establishment of acquired immunity in survivors and thus explai ns why survivors from natural infection are resistant to recurrence of the disease. Young sevenband grouper were immunized twice by intramuscular inje ctions with the recombinant coat protein. Immunized fish produced neutraliz ing antibodies at high titres for at least 110 days and showed significantl y lower mortalities in virus challenge tests. These results suggest the pot ential for vaccination against VNN in sevenband grouper, which is susceptib le to piscine nodavirus at all life-stages.